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IR-CUT of Camera Module

IR-CUT dual filter overview:

Why is there an IR-CUT?

There are various wavelengths of light in the IR nature. The wavelength range of light that the human eye recognizes is between 320nm-760nm, and the light beyond 320nm-760nm cannot be seen by the human eye; while the imaging components of the camera CCD or CMOS can see absolutely Most wavelengths of light. Due to the participation of various light, the color restored by the camera differs from the color seen by the naked eye. For example, green plants turn gray, red pictures turn light red, black turns purple, etc. At night, due to the filtering effect of the bimodal filter, the CCD cannot make full use of all the light, does not produce snowflake noise, and its low-light performance is unsatisfactory. In order to solve this problem, IR-CUT dual filters are used.

What is IR-CUT?

IR-CUT dual filter refers to a set of filters built into the camera lens group. When the infrared sensor outside the lens detects the intensity of the light changes, the built-in IR-CUT automatically switches the filter according to the external light The strength of the will automatically switch to make the image achieve the best effect. In other words, during the day or night, the dual filter can automatically switch the filter, so the best imaging effect can be obtained regardless of whether it is in the day or night.

2. The composition and working principle of the IR CUT dual filter switcher:

The IR CUT dual filter switch consists of an infrared cut-off low-pass filter (an infrared cut-off or absorption filter), a full-spectrum optical glass (a full-transmission spectrum filter), and a power mechanism (which can be electromagnetic, It consists of a motor or other power source) and a shell, which is switched and positioned through a circuit control board. When the daytime light is sufficient, the circuit control board drives the switcher to switch and position the infrared cut-off filter to work, CCD or CMOS restores the true color; when the visible light at night is insufficient, the infrared cut-off filter automatically moves away, full spectrum optics The glass starts to work. At this time, it can sense the infrared light of the infrared lamp, so that the CCD or CMOS can make full use of all the light, which greatly improves the night vision performance of the infrared camera, and the whole picture is clear and natural.

3. To distinguish between good and bad IR-CUT dual filter switcher:

a. The infrared cut-off degree of the filter, light transmittance, and light shaping effect, etc.

b. Power drive part

c. Control circuit

4. Filter:

In the daytime, CCD or CMOS simultaneously senses visible light and infrared light. The longer the wavelength, the smaller the refractive index; the shorter the wavelength, the greater the refractive index. Therefore, when these light rays enter the camera lens at the same time and are refracted by the lens lens, visible light and infrared light will be imaged on different target surfaces, while the imaging of visible light is a color image, and the imaging of infrared light is a grayscale image. The image formed by the visible light is well adjusted, which is the so-called lens rear focus adjustment and focusing. At this time, the infrared light will form a virtual image on the target surface, thereby affecting the color and quality of the image.

Generally, IR Coating or blue glass is used to filter out infrared light.

IR Coating is divided into vacuum coating and chemical coating. Electroless plating involves invading quartz plates into a solvent for electroplating. The cost is low, but the thickness of the plating film is uneven and easy to fall off. The vacuum plating uses a vacuum evaporation method. The thickness of the plating film is uniform and not easy to fall off, but the cost is relatively high. Due to the problem of infrared half-peak bandwidth, each product must be coated with a film that is compatible with it and cuts off different wavelength bands. IR Coating uses a “reflective” method to filter out infrared light, and reflected light can easily cause interference.

Blue glass uses “absorption” to filter infrared light, which is a better choice, but blue glass cannot be stored and used for a long time alone, because the physical layer on the surface of the blue glass is damaged during the cutting, polishing, and polishing process. Crystallization (commonly known as moldy) occurs, so we usually use two crystals and a blue glass. For example, the “three-piece” filter, in which IR Coating film or blue glass is used to filter out infrared light, and the crystal is used to trim the light to solve color bleaching (false color), and AR Coating coating is needed on the crystal to increase Transmittance.

About AR Coating:

Since the filter is not completely transparent, so-called AR Coating coating needs to be added to increase the light transmittance. In addition, AR Coating has the function of anti-oxidation and the function of adding protective film. The filter is protected by AR Coating and it is not easy to fog.

About Crystal:

Both CCD and CMOS are image sensors that use silicon photodiodes for light-to-electric conversion. They are composed of individual photoreceptors (CELL). It requires light to come in directly, and light coming in obliquely will interfere with neighboring light sensors. Color drift (false color) is generated, which requires the light to be trimmed. We use the physical polarization characteristics of the crystal to keep the direct part of the incoming light, and the oblique part of reflection and refraction to avoid the oblique light from affecting the photosensitive spot next to it. However, oblique light has different angles, and a piece of crystal can only handle oblique light in one direction. In theory, the more layers of crystals in different directions are stacked, the better the effect of solving color bleaching (false color). However, considering the actual demand and cost, generally only 1 to 3 pieces of crystal are used to solve the color bleaching (false color) problem of horizontal, vertical and 45° angle. There are so-called “two-piece” and “three-piece” filters, in which IR Coating film or blue glass is used to filter out infrared light, while crystal is used to trim the light, and AR Coating is required on the crystal. To increase light transmittance.

5. Power drive:

The IR CUT dual filter switch has a variety of driving methods and mechanisms, mainly divided into inductance coil type and motor type:

A. Inductance coil type is divided into coil movement or magnet movement. The coil driving method is small in size and low in cost, but the driving force is small, the self-locking ability is poor, the life of the coil movement is very short, and the life of the magnet movement is very long, the relative self-locking ability of the pendulum movement method is better, but it cannot drive large The size of the filter.

B. Motor type is divided into rack and pinion type, worm gear type and screw pair type. The spiral pair has compact structure, high power and strong self-locking force, which is a better choice.

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